Beacons Explained

RECCO, MLU, PLB, SPOT and Cellphones
Locating Beacons Explained

This article describes the various types of locating beacons in use, how and when they’re used, advantages and limitations, and current issues.

First, let me define the different types of beacons or locators; three which apply and three that don’t. There is a new device called a RECCO reflector that is often discussed alongside new locating technologies. Popular in Europe and growing in popularity here, these are tiny devices (passive diodes) that are sewn into clothing or built inside ski boots. A specialized RECCO detector transmits a signal which bounces back when the detector is pointed toward the reflector. They are used like an avalanche transceiver but differ in that they’re totally passive; there’s nothing the user needs to do. The detectors are not marketed to the general public and are typically used by ski areas to locate skiers caught in an avalanche. The signal travels well through air and RECCO is beginning to see use in helicopter scans of avalanche debris. On the ground, their operating distance is similar to that of an avalanche beacon, on the order of 30+ meters, so are not an option for ground searchers locating climbers lost on a mountain. New transceivers are getting smaller and also track avalanche beacon frequencies, so it’s possible the two technologies will someday merge. An avalanche beacon can be used for close-range searching but can not be used to find lost climbers so is not discussed in this article.

Locating beacons used to find lost climbers are the MLU (Mt Hood Locator Unit), PLB (Personal Locator Beacon) and SPOT (Satellite Personal Tracker). PLBs and SPOTs are similar to each other in that when activated, they’ll notify authorities via satellite and provide them with GPS coordinates. Both are about the same size and weight as an avalanche beacon. A PLB is a rescue-only device and transmits to an international satellite rescue system (COSPAS-SARSAT). Once activated, officials at Goddard Space Center notify the military, who in turn notify local authorities. This system is used around the world and is also used for marine and aircraft locators; PLBs are simply a land-based, handheld version of these long-used devices. PLB technology has advanced in the past decade, so be sure to understand the limitations of an older unit. A PLB also transmits a very low power homing signal that allows searchers to zero in the unit’s location. To save on limited satellite bandwidth, the last GPS location digit is dropped so the GPS location is only one-tenth as accurate. The reported location will be within about 100 meters–plenty accurate to find a lost boat or plane–but ground rescuers must rely on the homing signal to pinpoint a lost climber. PLBs also work in all four search phases. Detection and coarse location is done by satellite, while fine and pinpoint location is done by ground searchers using the homing beacon. A company called Safelife Systems, for an annual fee, now offers a notification service for PLBs, using the device’s Self Test feature to notify pre-programmed email and text-message addresses with a pre-determined message – similar to the SPOT’s “All OK” (see below).

A SPOT is consumer-oriented and communicates through the Globalstar satellite phone network. This is a commercial system (for-profit) with features such as Google Maps tracking and an “All OK” message sent to pre-programmed email or text-message addresses. Signal detection, coarse and fine positioning is all done by satellite, and is dependent on the quality of GPS signal received. There is no way for searchers to pinpoint a SPOT’s exact location, for example inside an unmarked snow cave. One nice feature of the SPOT is if Google Map tracking is being used, friends at home can tell something is amiss if the same location is repeated for an extended period. Some SPOT units can be tethered to a smart phone to allow two-way text communication. DeLorme is now marketing a similar system called inReach.

A big difference between the two systems is cost. PLBs currently cost $250 to $400 but do not require an annual fee. SPOTs are about $100 but have a $100/year annual fee, more if you want Google Map tracking or roadside assistance. PLBs require custom batteries and if activated, battery replacement costs nearly as much as a new unit; SPOTs use replaceable AAs–preferably lithium batteries due to their low-temperature performance.

Both systems require manual activation in case of emergency. Most people agree that the new satellite based locators are a big improvement over the old MLU technology. But whereas MLUs will work through snow and transmit for weeks, PLB/SPOTs use a higher frequency signal that is blocked by snow, and have a battery life once activated of only 1-2 days for PLB, and 3-4 days per set of AAs in a SPOT. It is recommended that the devices stay warm in order to preserve batteries (more on this below). Both are available for purchase at most outdoor stores but only available for rent by mail-order.

PLBs and SPOTs are two-way devices only insofar as they receive a high-frequency signal from a GPS satellite and transmit a lower-frequency signal to a communication satellite. There is no confirmation that the signal was received, so they’ll transmit multiple times. One received signal is all that is needed to initiate a rescue as well as communicate location. Unless timely rescue is certain, recommended emergency use for either unit is to leave it on only a few hours each day, and transmitting an emergency signal each day. This reduces drain on the battery, increases the chances of a signal being received, and also sends confirmation of your location and that you are still alive. Be aware that on the PLB this turns off the homing signal so if your exact location isn’t obvious, care must be taken in the hours chosen to turn the device off. Of course, wands, skis or flagging are always recommended to mark a snowcave’s location.

One issue being tested is the extent to which a snow cave will limit the functionality of PLB and SPOT units. Accuracy is only as good as the GPS signal received so they must reliably receive the high-frequency signal from GPS satellites. But the higher the frequency, the more the signal is blocked by water. As any GPS user knows, the location accuracy and time to get a reading is dependent on good signal quality. When used within snowcaves, the depth of the cave and density of the snow may impact GPS accuracy, or even preclude receiving any GPS signal. Initial testing indicates greater location error than would be required to pinpoint lost climbers. Further testing by PMR is ongoing. Until better results are known, it is recommended that when activated the devices are left outside in clear view of the sky, but placing them outside in the cold will decrease battery life.

Many Oregonians are familiar with the MLU, developed in the ‘80s by a private foundation with help from the Oregon legislature after nine people died in a snow cave. Using an adaptation of animal-tracking technology, the signal transmits through snow, can be picked up many miles away, and have batteries that will last weeks when activated. Their limitations are that they are line of sight only, must be manually activated, but most importantly, do not initiate a rescue. The signal is not monitored and a rescue must still be initiated by calling 911. Once confirmed that the party is carrying an MLU, searchers assemble the receiver and only then begin listening for a signal. Mount Hood is the only mountain in the world to have such a system. Because of their long distance and directional signal, an MLU can be used in all four stages of a search from signal detection through pinpoint location. The MLU technology, however, is becoming outdated by the higher utility of PLB and SPOT units. MLUs may be rented at the Portland REI and the Mountain Shop. You should call in advance to check availability. There is no place to obtain an MLU at Timberline Lodge.

Cell phones can also serve as locators for lost climbers. Although sometimes helpful for determining location, phones are more limited to two-way communication devices and should not be relied upon as a locating beacon. When 911 is called, the location is picked up by the operator; quite accurately with a GPS-enabled cell phone. But as every user knows, reception can be spotty outside of urban areas. On Mt Hood, cell phones often do not work anywhere other than directly above Timberline Lodge. A GPS and a cell phone can be a good combination, but only if the phone has service. Although of limited accuracy, cell towers can triangulate phone location based on the signal received from multiple towers. For this to work the phone must be turned on, the phone company must cooperate and if the phone is having trouble connecting to one tower, it is unlikely to connect to multiple towers. The obvious advantage of a cell phone is when it does work, it offers true two-way communication. For further information, please read our Cell Phone as a Rescue Resource fact sheet.

The last solution is probably the most effective, but also the most expensive and least used and isn’t really a locating beacon. That would be a combination of satellite phone and GPS. Although still requiring activation by the lost or injured party, it offers true two-way communication and fine search resolution through the reported GPS coordinates. The only limitation is that should the lost subject move or be unconscious, there is no way to confirm or pinpoint their location without verbal communication.

For the back country travels, there still is no best choice for emergency locator systems, and no emergency locator system should be relied upon to save your life. Lost climbers are often lost due to storms, when it can take days to reach them, even if they can effectively send a distress signal. During that time, survival is critical. Items such as shovel, pad and stove can keep you alive, but a beacon won’t. Always make sure you bring critical survival gear, then pack the beacon, too.

Additional Reading:

Here are some handy weblinks with more information on the items discussed above.